The present invention relates to a composition stable in the state containing water, which, upon application to the scalp, activates melanocytes of the radix pili and promoting synthesis of melanin, thereby preventing graying of the hair and restoring grayed hair to its natural color.
Graying of the hair is a universal aging phenomenon, while hair dyes are commonly used to dye grayed hair, the use of such dyes is troublesome and sometimes causes side-effects such as rash of the scalp. Therefore, many users find hair dyes to be an unsatisfactory solution of the graying of the hair.
Under such circumstances, it has been desired to develop a pharmaceutical preparation or a cosmetic composition for application to hair capable of essentially preventing graying of the hair and restoring grayed hair to its natural color.
Heretofore, there have been some proposals such as those described in Japanese Patent Un-examined Publication (hereinafter referred to as "J.P. KOKAI") Nos. 60-174705, 61-165310, 62-45527, 62-63509 and 62-63510 in compliance with such a demand. However, the proposed techniques suffer from various disadvantages such as low effectiveness, low stability of the active components and insufficient safety. Among these, J.P. KOKAI No. 62-45527 discloses the use of adenosine 3',5'-cyclicphosphoric acid compound (hereunder referred to as "cAMP") and derivatives thereof.
However, this method suffers from the following problems:
(i) cAMP and salts thereof exhibit only a low cell membrane permeability and even if they are absorbed into cells, they are likely to be decomposed by phosphodiesterase, therefore, they do not show sufficient effect of preventing graying of the hair and restoring grayed hair to its natural color.
(ii) Acyl derivatives of cAMP are unstable in a composition for use in external applications and are easily decomposed with time. Therefore, if they are used as an agent externally applied over a long period, sufficient effects cannot be expected.
(iii) Moreover, the acyl derivatives of cAMP give out bad smell due to decomposition.